Morphology-controllable ZnO nanotubes and nanowires: synthesis, growth mechanism and hydrophobic property

Controlled growth of nanostructures has long been regarded as one of the biggest obstacles to their commercial applications. Herein we demonstrate the feasibility of controlling growth of ZnO nanotubes and nanowires by floating substrates on the surfaces of reacting solutions with different concentrations, a key factor for differential growth. These slim ZnO nanotubes with outer diameters of 26.6 ± 12.2 nm and inner diameters of 8.3 ± 6.2 nm (confidence level of 95%) are a recently discovered new class of nanostructures whose growth is driven by screw dislocations (S. A. Morin et al., Science2010, 328, 476–480). Concentrations of precursors below 0.5 mmol L−1 adequately allow the slow relocation of solute clusters and spontaneous formation of the single crystal tube while the concentrations above 15 mmol L−1 induce high-speed deposition of newly forming solute clusters and fast growth of nanowires; therefore the concentration plays a crucial role in determining the morphology of one dimensional (1D) ZnO nanostructures. Furthermore, the ZnO nanotube surface, which apparently displays smaller dimension and lower density of nanostructures, exhibits improved hydrophobic property compared to the ZnO nanowire surface. The large scale controlled growth of arrays with different 1D ZnO nanostructures should be essential for fabricating novel devices and exploring advanced applications.